The tumor antigen (protein) of Dorsett et al (1) will be investigated for the purpose of developing a radioimmunoassay capable of detecting ovarian carcinoma by a serum test. Rabbit antisera to intact ovarian tumors and pooled tumor homogenates will be serially absorbed with normal tissue antigens. Such antisera have been shown to be ovarian tumor specific, and may be used in an immunodiffusion assay. Pooled ovarian tumors will be sonicated and the insoluble proteins removed centrifugally. The antigen will be initially purified by perchloric acid and salt precipitation procedures. Column chromatography and isoelectric focusing will be utilized to effect final purification. Rabbit and goat antisera to the purified antigen will be raised for the radioimmunoassay. The cross reaction, if any, of these antisera with normal or non-ovarian tumor antigens will be explored. The radio- labeling of the pure antigen will permit its use in a competitive binding assay. Separation of the bound and unbound antigen will be made by salting-out techniques or through use of gel-insolubilized antibody. The organ specificity of this protein will be examined by correlation of assay results on tissue and serum for a wide variety and large number of patients with their clinical and morphological data. Physical-chemical characterization will provide a basis for understanding the relation of ovarian tumor protein to normal cellular constituents.